Correction of ionic recombination for pulsed radiation according to DIN 6800-2 and TRS-398

The international Agency of Atomic Energy (IAEA) has recently published a new code of practice (TRS-398) for dosimetry of ionizing radiation. In this code, the saturation correction for pulsed radiation is treated differently compared to the German regulation DIN6800-2. The Code provides also an approximation formula that is not identical to that of DIN 6800-2. The present study analyzed the relations between the different formulas and determined the impact on the size of the resulting saturation correction factor. All formulas can be traced back to Boag's theory of ionic recombination, however the formula in DIN 6800-2 uses an additional linear approximation. The approximation in TRS-398, in turn, can be derived from the formula in DIN 6800-2 by applying a further linear approximation. Measurements were performed with four different ionization chambers using photon and electron beams. All formulas yielded the same saturation correction within 0.1%. However, for the medical physicist in a hospital it would be desirable to have the same formula in national regulations and international recommendations, to avoid any uncertainty on which method to apply.